I have simulated my structure using NAMD. later I converted the .dcd file to xtc. i tried to run the gmx covar command but it is giving error to use .tpr file. I have tried to use .gro file but I am still getting the same error.
To get a .tpr file for analysis, you might want to convert your topology from NAMD format into Gromacs first (try ParmEd) and use gmx grompp with the topology, the .gro, and a sample mdp file. Run gmx grompp -h for a list of required inputs.